Conventional articles of footwear, including athletic footwear, typically have included two primary elements, namely an upper member and a sole member or structure. The upper member provides a covering for the foot that securely receives and positions the foot with respect to the sole structure. In addition, the upper member may have a configuration that protects the foot and provides ventilation, thereby cooling the foot and removing perspiration. The sole structure generally is secured to a lower portion of the upper member and generally is positioned between the foot and the ground (as used herein, the term “ground” includes any type of foot or footwear contact surface, including but not limited to dirt, grass, sand, tile, flooring, carpeting, artificial turf, etc.). In addition to attenuating ground reaction forces, the sole structure may provide traction and help control foot motion, such as pronation. Accordingly, the upper member and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole member or structure of athletic footwear, in at least some instances, will exhibit a layered configuration that includes a comfort-enhancing insole, a resilient midsole (e.g., formed, at least in part, from a polymer foam material), and a ground-contacting outsole that may provide both abrasion-resistance and traction. The midsole, in at least some instances, will be the primary sole structure element that attenuates ground reaction forces and controls foot motion. Suitable polymer foam materials for at least portions of the midsole include ethylvinylacetate (“EVA”) or polyurethane (“PU”) that compress resiliently under an applied load to attenuate ground reaction forces. Conventional polymer foam materials are resiliently compressible, in part, due to the inclusion of a plurality of open or closed cells that define an inner volume substantially displaced by gas.
To keep a wearer safe and comfortable, footwear is called upon to perform a variety of functions. For example, the sole structure of footwear must provide adequate support and impact force attenuation properties to prevent injury and reduce fatigue, while at the same time provide adequate air exchange and breathability to provide a comfortable housing for prolonged wear under athletic use conditions. Given the multiple requirements for footwear products, it would be useful to provide a sole structure and/or support elements included as part of a sole structure that provide adequate strength and support while still providing a breathable structure that allows for relatively free air exchange between the interior and exterior of the shoe.